The long-term goal of this laboratory is to understand the function osteoclasts in the process of bone resorption. the purpose of this application is to elucidate the regulation of H+ generation by osteoclasts. H+ generation will be detected by measuring levels of acridine orange fluorescence in osteoclasts isolated from the endosteum of tibia and other long bones. Three sources of osteoclasts will be used: 3-week-old chicks on a normal calcium diet, 3-week chicks on low calcium intake, and day-old rabbits. This will allow comparison of avian and mammalian models. Specifically, the signal transducers (e.g., G-proteins) and effectors (e.g., adenylate cyclase, phospholipase C, Ca2+ channels) for parathyroid hormone (PTH), calcitonin and prostaglandin E2 will be investigated. Osteoblast-osteoclast interactions will be studied, particularly with regard to PTH effects. Estrogen and androgen effects on H+ generation by osteoclasts will be examined. Finally, specifically bound PTH and calcitonin to osteoclasts will be studied by biotin-strepavidin-gold labeling in order to characterize receptor-mediated endocytosis of these two important regulators of osteoclasts. Understanding the mechanism of action of osteoclasts has relevance to disease with an involvement of bone loss, such as periodontitis, osteoporosis, osteoarthritis and end stage renal disease. Osteoclasts are also important in normal bone turnover and in tooth eruption and movement.